1. Field of Invention
The present invention relates to a sensor pixel of a touch panel, and more particular, utilizes the sensor pixel having a photo transistor to detect a location of the finger.
2. Description of the Related Art
With great advance of electronic technique and popularity of wireless communication and internet, the portable devices having light, thin and small advantages gradually become a data access platform in a new generation. Nevertheless, not all the equipments have common usage input and output (I/O) interfaces for human, such as keyboards or mice. Hence, the touch panel is often applied to be a human-machine interface between human and intelligent equipments for controlling.
Generally, the resistive touch panel is composed of two conductive layers separated by thin space. When users press the touch panel, the layers are connected at certain point and thereby a voltage variation corresponding to the certain point is generated. Through converting the analog signal with the voltage variation into a digital signal by analog to digital converter (ADC) and processing the digital signal, the coordinates of horizontal and vertical axes of the pressure point can be located. However, the resistive touch panel gets damaged easily by frequently pressing because of having no protective film, and only a single pressure point can be detected on the resistive touch panel. If there is a plurality of pressure points, i.e. multi-finger, the resistive touch panel is not able to determine the actual position of the pressure point. Besides, disposing the layers not only increases the thickness of the touch panel, but also affects the light transmission for liquid crystal display (LCD). Furthermore, the resistive touch panels can not precisely locate the positions of the pressure points. Consequently, the resistive touch panel cannot satisfy the requirement of consumers.
Another type of touch panel is the optical touch panel utilizing a plurality of infrared transmitters and infrared receivers disposed around it, that is, the infrareds produced from the infrared transmitters in the horizontal and vertical directions forms an array arrangement. When an opaque object obstructs one of the infrareds transmitting, the position of pressure point in horizontal and vertical axes is located. However, the optical touch panel is sensitive to even a tiny object or external light disturbance, and this matter causes incorrect position detection. Therefore, the factories and stores extremely make effort on designing the touch panel that can solve the said problems and overcome the disadvantages.